inner iron skin a short distance from the outer bottom. In case of the latter being punctured, the inner skin would prevent an influx of water to the interior of the ship. This was first carried out in the 'Warrior,' but the dual portion only extended 11 ft. on each side of the keel. In succeeding ships this principle was developed, and the inner skin became a veritable second hull under water, the space between the two being increased and sub-divided into a number of cells. This cellular sub-division was adopted with the view not only of giving strength in case of striking the ground, but also of reducing the effect of a torpedo explosion under water. As it was impossible to place armour here, the double bottom was a substitute, the hope being that the inner skin would be intact after the outer hull had been driven in by the explosion. As against the blow delivered by a ram such a protection would be insufficient. The only safeguard is to divide the interior of the vessel into watertight compartments, so as to confine the water which would rush in when both skins were fractured to that particular locality. This principle had been carried out in greater degree with succeeding ships, so that the 'Inflexible' had 127 of these compartments. Each is provided with a watertight door, to allow free access to all parts at ordinary times, and these, of course, must be a source of weakness to the principle. They may not be closed at the proper time, and are liable to get out of order unless continually worked.
Although the difference in weight between four 38-ton
